Cataphoretic application of coatings



Jan. 11, 1955 M. C. HOFFMAN 2,699,426

CATAPHORETIC APPLICATION OF COATINGS Filed Sept. 30, 1949 w MIL-TONC. HOFFMAN YWW . ATTORNEY United States Paten p CATAPHORETIC APPLICATION OF COATINGS MiltonC. Hoffman, Emporium, Pa., assignor to Sylvania 7 Electric Products linc.,-a corporation of Massachusetts Application September 30, 1949, Serial No. 118,809

2 Claims. (Cl. 204-181) The present invention relates to the application of coating material to conductive supports and more particularly to the cataphoretic coating of finely divided solid particles contained in a liquid suspension onto conductive supports.

An object of the present invention is the provision of a novel arrangement for coating emissive material onto a conductive filament.

Another object of the present invention is to provide a novel manner of coating materials onto a conductive support which will replace the previously known method of spray coating.

A further ob ect of the present invention is the avoidance of the substantial loss of coating material and coils due to imperfect masking or entangling of the coils, abraded and cracked coatings, and physical destruction due to handling difficulties which has characterized previously known methods of coating filament coils.

Still another object of the present invention is the provision of a novel method of manufacturing electron tubes wherein the filament mount is completely assembled except for the emissive coating and thereafter the emissive coating is applied to the coil surface alone using the mount as the handling and electrically conducting support. After the emissive coating is applied the mount is then ready for sealing without subsequent mechanical operation. Losses due to handling are thereby minimized.

Still a further object of the present invention is the reduction in cost of coating emissive material onto coil filaments.

Still a further object of the present invention is the simplification of the manufacture of electron discharge devices.

The foregoing objects and others which may appear from the following detailed description are attained in accordance with an aspect of the present invention by dipping the already coiled filament, attached to a con ductive support into a vertically emergent stream or fountain of coating suspension discharging from a pumping device. An electrical potential is applied between an electrode in the body of the suspension and the conductive support immersed in the fountain thereof for a controlled period of time. As a result of the current which flows in the circuit thus established finely divided solid particles contained in the suspension attach themselves to the conductive support or to other like particles so attached and thus provide a closely adherent dense coating of material on the filament, said coating being substantially uniform and complete irrespective of the physical form of the conductive support.

The present invention will be more fully understood by reference to the following detailed description which is accompanied by a drawing in which Figure l illustrates in a perspective view an embodiment of the present invention while Figure 2 is an elevational view in section showing the interior construction of the device shown in Figure 1.

In the drawing there is shown a bath or tank 10 containing a liquid suspension 12 of the desired finely ground coating material suspended in a solvent of high dielectric strength. Supported immediately above the bath 10 containing the suspension and dipping into the bath is an Archimedean pump including a vertical cylinder 14 having a rotating spiral 16 therewithin. The ro tating spiral 16 is adapted to be rotated by shaft 17 driven by a suitable motor (not shown). Rotation of 2,699,426 Patented Jan. 11, 1955 the spiral 16causes the suspension 12' to be drawn up within thetube 14. Other forms of pumping devices may be used if desired. The liquid is discharged into a lateral tube 18which connects with a vertically extend ing', vertically directed nozzle20. A needle valvetarrangement22 is provided by means of which the volume and height of the stream emerging from-the nozzle 20 may be controlled. In order to assure a continuous flow of the cataphoretic suspension from the bath 10, the upper end of tube 14 is provided with an overflow tube 24 by means of which surplus fluid not passing through tube 18 and nozzle 20 is returned to the bath 10. The nozzle 20 extends through an aperture 26 in a table 28, preferably of insulating material. The coating material which emerges from nozzle 20 drops back through aperture 26 and falls into the bath 10. Thus a constant circulation of the coating suspension is provided.

The filament to be coated with the suspension is shown in Figure 1 at 30. It is previously assembled to a pair of support wires 32 and 34, one of the wires being connected to stem shield 36 of the mount while the other is insulatingly held in a position generally parallel to the first. A unitary mount assembly is thus provided which may subsequently have wires 32, 34 sealed through a header of an electron tube. A conductive seat 40 is provided on table 28 so positioned that when the stem shield 36 is positioned in the support the filament 30 is supported directly above nozzle 20 and within the emergent jet or stream of material. The positioning of the stem shield 36 in the mount 40 depresses an actuating leaf 42 of a normally open switch indicated generally at 44, whereby a circuit is completed from a source of potential as indicated by the arrow labeled to power supply through timer 45 through the closed contacts of switch 44, the base shield supporting member 40, base shield 36, one of the conductors 32, 34, filament 30, through the jet of coating material emerging from nozzle 20 and through the remainder of the coating suspension material or the metal tubes 18, 14 to the other side of the power supply. As mentioned before the straight filament coil 3-0 of the otherwise completed mount is positioned by the mounting support 40 acting as a jig so that the emergent jet of coating suspension material from nozzle 20 covers the portions of the coil to be coated. This positioning is substantially mechanically controlled as the operator places the mount in the jig. Placing the mount in the jig also actuates the electrical switch 44 which provides for the closing of the electrical circuit for an accurately determined time period controlled by the timer 45. At the end of the time period the completed mount is removed from the coating device and immediately the filament coil is dipped momentarily in a solution of diethylcarbonate to effect the removal of the excess non-adherent coating and finally in petroleum ether to complete the removal of excess material and to accelerate the subsequent air-drying. I have found that the time period of the coating application will vary to some extent with the particular suspension and the coating thickness requirement, but the time interval on the order of one-and-a-half seconds has proved satisfactory. The subsequent rinsing operations normally are accomplished in time periods of one-half to three seconds each.

While the coating suspension may be any suspension of finely divided solid particles in a solvent of high dielectric strength such that movement of the solids occurs with an impressed potential, I prefer that the suspension should be one of the varieties indicated in prior Patents 2,442,863 and 2,442,864.

While I have shown and particularly described one embodiment of the present invention, it should be clearly understood that my invention is not limited thereto but that1 modifications within the scope of the claims may be ma e.

What I claim is:

1. In the manufacture of electron discharge devices the method of preparing a mount structure which comprises assembling an uncoated filament wire to a support structure of said electron discharge device, positioning only the portion of said filament which is to be coated within a jet of a suspension of coating material in a liquid, said jet having a cross-section which is long and narrow with the long dimension parallel to the length of the wire and passing an electric current through said material and said filament whereby said material is electrophoretically deposited on said filament.

2. The method of electrophoretically applying a coat ing material to an elongated conductor which comprises supporting said conductor in a jet of a liquid suspension of said material, said jet having a crosssection which is long and narrow, the conductor being aligned with the long cross-sectional dimension of the jet and passing an electric current through said conductor and said suspension.

References Cited in the file of this patent UNITED STATES PATENTS Bailey May 23, Waldschmidt Oct. 8, Buckman et a1. Aug. 11, Cardell Jan. 5, Schneider June 8, Waterman Apr. 4,

FOREIGN PATENTS Great Britain May 21, 

2. THE METHOD OF ELECTROPHORETICALLY APPLYING A COATING MATERIAL TO AN ELONGATED CONDUCTOR WHICH COMPRISES SUPPORTING SAID CONDUCTOR IN A JET OF A LIQUID SUSPENSION OF SAID MATERIAL, SAID JET HAVING A CROSSSECTION WHICH IS LONG AND NARROW, THE CONDUCTOR BEING ALIGNED WITH THE LONG CROSS-SECTIONAL DIMENSION OF THE JET AND PASSING AN ELECTRIC CURRENT THROUGH SAID CONDUCTOR AND SAID SUSPENSION. 